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By W. S. Owen, T. Bell

The variation ox the M, temperature with nitrogen concentration has been determined experinzentally. The free-energy difference between martensite and the parent y Phase at the M, temperature,is computed for Fe-C and Fe-N alloys using recent solubility data fm the Fe-N system and new data for the variatim of the activity of the interstitial solute in the y phase with concentration. The "geometric model" is considered also, and the importance of Zener ordering is noted. It is shown that, although at any chosen concentration the M, temperature and the activity are significantly different in the two alloy systems, the free-energy duference is the same within the limits of experimental error, thus Providing further evidence of the very close similarity between the martensite transformations in Fe-C and Fe-N alloys. TO estimate the free-energy change accompanying the martensite transformation in binary interstitial alloys it is necessary to know the variation of the Ms temperature with interstitial solute concentration and some thermodynamic data. To date, only the Fe-C system has been discussed because this was the only system for which relevant experimental measurements had been made, but even in this case the data available are insufficient to permit the free-energy change to be calculated without the assumption of a thermodynamic model for the y and a solid solutions. The last comprehensive discussion of the topic was by Kaufman, Radcliffe, and Cohen in 1.960.' Since that time Ellis, Davidson, and Bodsworth2 have redeter mined the activity of carbon in y iron as a function of carbon content and Atkinson3 has measured the activity of nitrogen in Fe-N austenite. The M, temperature of Fe-N is reported in the present paper. Thus, it is now possible to assess the free-energy change accompanying the martensite transformation in Fe-N alloys on the same basis as that used to assess the change in Fe-C alloys. This comparison is of interest because it has been shown recently4 that the structure of the martensite formed in Fe-N alloys changes with nitrogen content in a manner exactly parallel to the changes in structure in the Fe-C series and that the strain associated with the distortion of the iron lattice in either the y or the a phase by a nitrogen atom is the same as that produced by a carbon atom. The work to be described tests whether or not this close similarity between the two systems extends to the thermodynamics of the martensitic transformations. THE Ms TEMPERATURES FOR Fe-N MARTENSITE Bose and Hawkes5 found the M, temperature of a eutectoid Fe-N alloy (2.35 wt pct N) to be 35°C. This single determination appears to be the only reported measurement of the M, temperature of an Fe-N alloy. In the present work a series of more than fifteen different specimens containing between 0 and 2.7 wt pct N were prepared by controlled nitriding of pure iron wire 0.010 in. diam. The iron was supplied by B.I.S.R.A. and was designated ACN2. The nitriding procedure, all aspects of which are critical, has been described in detail elsewhere.' Each specimen was quenched from the austenitizing temperature into brine at 20°C without removing the specimen from the ammonia-hydrogen atmosphere in which it was ni-trided. Alloys containing up to 0.7 wt pct N were fully martensitic. More concentrated alloys contained progressively more retained austenite. At 2.34 wt pct N the specimen was completely austenitic after quenching to 20°C. The M, temperature of specimens with M, temperature above 20°C (those containing less than 2.35 wt pct N) was determined by a thermal arrest technique. For the more concentrated alloys (2.35 to 2.70 wt pct N) the variation of electrical resistance with temperature down to -196°C was used. Unlike Fe-C alloys, Fe-N alloys cannot be reaus-tenitized in vacuum or in an inert atmosphere because excessive loss of nitrogen occurs, even in short times, at high temperatures. Consequently, the alloys were reaustenitized in the ammonia-hydrogen mixture corresponding to nitrogen equilibrium at the temperatures used. The specimens were quenched in a blast of cold hydrogen gas and the temperature, measured by a thermocouple welded to the 2.5-in.-long specimen, was recorded on a high-speed recorder. In the first experiments 0.002-in.-diam chromel-alumel wire thermocouples were used but it was found that these gave erroneous readings due to contamination by nitrogen pickup. Pt-Pt 13 pct Rh wires of 0.002 in. diam were found to be satisfactory. Further details of the experiments are available in the original thesis.7 The cooling rate was controlled between 400° and 4000°C per sec by adjusting the hydrogen pressure. At least three cooling curves were obtained for each composition. Each specimen was analyzed for nitrogen after quenching. To aid in the accurate location of the martensite arrest points a series of cooling curves of 0.010-in.-diam platinum wire were recorded and these, which did not contain an arrest, were used as comparison standards. Four specimens, each in the form of a 3-in. loop, were prepared from each of the four alloys containing more than 2.35 wt pct N. One specimen was used for nitrogen analysis, one for X-ray diffraction, and two for resistance measurements below 20°C. The latter specimens were quenched from 20°C into constant-temperature baths at selected lower temperatures.

Jan 1, 1968

By Robert W. Thomas

LEACHING of mined-out areas at the Arizona property of the Ray Mines Division, Kennecott Copper Corp., was started on Jan. 20, 1.937, and by July 1, 1938, 10,000,000 lb. of copper had been produced by this method. Leaching operations at present are confined to the western portion of the ore body and over an area of approximately ten acres. The ore in this area was extremely high in pyrite and the copper content, which averaged slightly in excess of 1 per cent, was the result of incomplete secondary enrichment by solutions which apparently worked laterally from the main ore body. Above the ore was an unaltered zone of primary or protore averaging 125 ft. in thickness and containing approximately 0.6 per cent copper. Above this was the capping or leached zone averaging 50 ft. thick.

Jan 1, 1938

ALABAMA. Aldrich.-Aldrich, W. F. Anniston.-Noble, A. E., 20th St. and Wilmer Ave. Auburn.-Brown, R. L., Box 0. Bessemer.-Abbott, C. E., T. C., I. & R.R. Co. Ferguson, V., U. S. C. I. Pipe & Fdy. Co. Williams, E. P., Tenn. C., I. & R. R. Co. Birmingham.-Aldricb, T. H. Aldrich, T. H., Jr., 406 Woodward Bldg. Allen, A. W., 1616 S. 14th Ave. Bowron, J., 1401 S, 20th St. Burbidge, T. A., Browu-Marx Bldg. Coxe, E. H., Tenn. C., I. & R. R. Co. Crawford, G. G., Tenn. C., 1. & R. R. Co. Crockard, F. H., Woodward Bldg. Dimmick, F. D., Dimmick Pipe Co. Ellis, E. E., 1515 Brown-Marx Bldg. Fairbairn, C. T., Woodward Bldg. Fies, M. H., 2316 Highland Ave. Hiller, E., 516 Brown-Marx Bldg. Hillman, M. P. G., 707 Empire Bldg. Ludwig, C. P., 12th Ave. and 12th St. McCormack, G. B., Lookout Mt. Iron Co. McCrery, C., Tenn. C., I. & R. R. Co. Moffett, C. A , 909 Brown-Marx Bldg. Peters, R.. Jr., Brown-Marx Bldg.

Jan 1, 1917

By S. R. Titley

The recent emphasis placed upon the use of molybdenum as a geochemical indicator has stimulated considerable inquiry into the behavior of molybdenum in the zone of oxidation. This paper represents a summary of recent and continuing experimental work and calculations in an investigation of a portion of the system Mo-Fe-S-H20 and treats the stability of various iron and molybdenum compounds with respect to oxidation potential and pH. Using experimentally determined free energy values for ferrimolybdite, diagrams of the stability fields of this mineral have been calculated with respect to ilsemannite (?), molybdenite, pyrite and limonite. This theoretical approach is the one utilized by Garrels3'4 in studies of the relationships of various minerals in the zone of oxidation. Use of this approach is particularly suited to the study of geochemistry in the zone of supergene processes because of the low temperatures, low pressures and other relatively easily determined and duplicated factors that exist in the near surface environment. Such a study of molybdenum, however, is complicated by several factors. One of these is the fact that the strong amphoteric behavior of molybdenum makes possible a wide variety of substances and complexes whose exact chemical natures are unknown. The second factor is the dearth of thermodynamic data for many of the simplest of the possible compounds and ions important to the study. For the purpose of this study, the problem of complexes has been approached through considering only the simpler possibilities realizing that the complexes and systems so treated may be gross oversimplifications. All the complexes considered, however, have been suggested in the chemical 2,7,9,12 or geologi-cal literature. EXPERIMENTAL WORK Studies of the behavior of molybdenum ions and ferrimolybdite have been carried out in aqueous sys- tems, and reactions have been followed by simultaneous measurement and recording of pH and oxidation potential. A major problem involved in this study was the long periods of time necessary for equilibrium to be established in some of the systems considered; in a few instances, these periods exceeded four weeks, that is, four weeks during which measured conditions changed continuously. Another problem, in some instances, was the indeterminate nature of the reactions that have taken place. Because of the tendency of molybdenum to complex, reactions which take place under some of the more extreme imposed conditions of oxidation and acidity or alkalinity are unknown. However, useful data for the present work were obtained from studies of the molybdate ion and ferrimolybdite between pH 2 and 8 and under only moderately oxidizing to nonoxidizing conditions. Instruments used in the experiments were a Hewlitt-Packard Model 412A VTVM, a modified Beckman Zeromatic pH Meter and two Varian model 11 recorders. pH was measured between glass and calomel electrodes and Eh was measured between calomel and platinum electrodes. Conditions of pH were varied with 1N H2SO4 and 1N NH4OH and 1N NaOH. Eh was varied with gaseous nitrogen, oxygen or aqueous H202. Ambient temperature was essentially uniform at 24ºC and was increased in the reaction vessel by the positioning of a magnetic stirrer whose temperature was sufficient to bring the temperature to 2S°C in the reaction. The temperatures of reaction did not vary more than 1/2ºfrom 25°C. Two reactions were investigated, the ferrimolybdite-limonite-water reaction and the reduction of molybdate ion. Studies of both reactions yielded useful data that were used in preparation of the Eh-pH diagrams. The traces of the reactions are shown on Fig. 1. Ferrimolybdite-Limonite- Water: Studies of this reaction involved analysis of the solution of ferrimolybdite and simultaneous formation of ferric hydroxide. The data are summarized on Fig. 1. In this reaction, equilibrium was attained at various pH's when coexistence of the two solid phases (ferrimolybdite and ferric hydroxide) was attained. At the proper pH, controlled by the amount of ferrimolybdite and thus the dissolved content of molybdate species, both phases were observed and reaction times to complete the transition were on the order of weeks. The reac-

Jan 1, 1963

By B. W. Howlett, M. B. Bever, Somnath Misra

The heats of Formation of the compounds Sb2Se3, Bi2Se3, Sb2Te3, and Bi2Te3 and the heats of solution of tellurium and selenium in liquid bismuth have been measured in a liquid metal solution calorimeter. The heat capacities near the melting point, the heats of fusion, and the melting points of the two tellurides have been measured in a constant temperature gradient calorimeter. The thermo-dynamic quantities are interpreted in relation to the stability of the compounds and the nature of the solid-liquid transition. THE selenides and tellurides of several elements of Group VB of the periodic system are of interest because of their electronic properties. The compounds Sb2Se3, Bi2Se3, Sb2Te3, and Bi2Te3 are semi- conductors; they also have gained prominence in the fields of thermoelectricity and photoconductivity. However, little is known about their thermody-namic properties. As part of a research program on the thermo-dynamic properties of intermetallic compounds, the heats of formation of the compounds Sb2Se3, Bi2Se3, Sb2Te3, and Bi2Te3 were measured in a liquid metal solution calorimeter. The heat capacities near the melting point, the heats of fusion, and the melting points of the two tellurides were measured in a constant temperature gradient calorimeter. The results, in addition to their intrinsic interest as thermodynamic quantities, contribute to an understanding of the stability of the compounds and the nature of the solid-liquid transition. 1) EXPERIMENTAL 1.1) Materials. Samples of the compounds SbzSe3 and Bi2Se3 were prepared by melting the elements in stoichiometric proportions in evacuated Vycor capsules followed by quenchinn in water. They- were then annealed in vacuum for 12 hr at 550°C. A sample of Sb2Te3, consisting mainly of one large grain, supplied by the Lincoln Laboratory,

Jan 1, 1964

By R. H. Hadfield

Professor ArnolD, of the Sheffield Technical School, who has done so much excellent work in metallurgical research, recently produced, with the aid of aluminum, a sound ingot and bar from the purest known Swedish brand containing 99.8 per cent. of pure iron. Table 1. shows the physical quantities of this metal. TABLE I.— Tests of a Sample of Almost Pure Iron Prepared by Professor Arnold from D. v Ewedish Bar, Containing Before Fusion 0.04 Per Cent. of Carbon. I. II.+ III. Series mark,.. 136 1.371F ...... C, 0.07 0.07 Si, 0.04 0.04 8, 0.02 0.03 ...... Analysis, per cent,. .. P, 0.02 0.015 ...... Mn, 0.06 0.07 Al, 003 ............ Fe, 99.76 99.81 ...... Specific gravity,........... 7.863 ...... Original diameter, inches,. .. 0.564 0.798 0.798 Original area, square inches,. . 0.25 0.50 0.50 Limit of elasticity, tons per square inch,...... 18. 3.8 Breaking-load, tons per square inch,. 21. 23. 14.75 Total elongation, per cent., measured on 2 in.,...... 50. 49.25 61. Total reduction of area, per cent.,. 80. 69.60 61.20 Extension at permanent set, per cent.,...... 0.007 ...... silky and Appearance of fracture,. .. . silky i granular in parts.

Jan 1, 1894

By Charles R. Austiuon, Carll H. Samans

It has been known for several years1 that certain alloys of the Konal type, containing commercial cobalt (99.32 per cent Co and 0.42 per cent Ni) and varying amounts of ferrotitanium, exhibit very high tensile strengths at 600°C. However, their proportional limits and yield pints are relatively low. published data' for the alloys quenched in water from 950°C. and then tested at 600°C. are summarized in the upper section of Fig. I. Similar specimens that were aged at 650°C. for 72 hr., after quench and prior to testing at 600°C., gave the result; shown in the: lower section of Fig. I. In the present work the investigation of the properties of these materials has been extended by a study of the tensile deformation characteristics in moderately longtime tests at 600°, 700' and 800°C. after quenching from various solution temperatures. In addition, some metallographic studies have been made to correlate with the deformation tests, and to obtain information on the quasi-binary system cobalt-Fe2Ti. The material, very kindly furnished by the Westinghouse Electric and Manufacturing Co. in the form of hot-swaged rods of 3/16-in. diameter, analyzed as shown in Table 1. The alloys, when originally made up,' were based upon an iron-titanium compound, Fe3Ti, as indicated by the work of

Jan 1, 1941

By Carll H. Samans, Charles R. Austiuon

It has been known for several years1 that certain alloys of the Konal type, containing commercial cobalt (99.32 per cent Co and 0.42 per cent Ni) and varying amounts of ferrotitanium, exhibit very high tensile strengths at 600°C. However, their proportional limits and yield pints are relatively low. published data' for the alloys quenched in water from 950°C. and then tested at 600°C. are summarized in the upper section of Fig. I. Similar specimens that were aged at 650°C. for 72 hr., after quench and prior to testing at 600°C., gave the result; shown in the: lower section of Fig. I. In the present work the investigation of the properties of these materials has been extended by a study of the tensile deformation characteristics in moderately longtime tests at 600°, 700' and 800°C. after quenching from various solution temperatures. In addition, some metallographic studies have been made to correlate with the deformation tests, and to obtain information on the quasi-binary system cobalt-Fe2Ti. The material, very kindly furnished by the Westinghouse Electric and Manufacturing Co. in the form of hot-swaged rods of 3/16-in. diameter, analyzed as shown in Table 1. The alloys, when originally made up,' were based upon an iron-titanium compound, Fe3Ti, as indicated by the work of

Jan 1, 1941

By A. B. Kinzel

SILICON and its metallurgical uses have been the subject of speculation since the earliest days of modern civilization. The early philosophers, Theophrastus and Pliny, believed that silica was a special form of ice, an opinion that was not seriously challenged until the seventeenth century. The first comprehensive view of the nature of silica was advanced by Lavoisier in 1787. He assumed silica to be an oxide of an unknown metal. In 1808 Berzelius produced ferrosilicon by heating silica, iron and charcoal. Probably the first produc¬tion of crystallized silicon was in 1854 when H. St. C. Deville accidentally produced the material while electrolyzing a double chloride of aluminum and sodium containing siliceous impurities. It is not strange that the early investigators should have given so much attention to silica and silicon, because of the great natural abundance of the former. Although silicon does not exist in the elemental state in nature, it has been estimated that the lithosphere contains approximately 60 per cent silica; quartz and rock crystal are found in practically every part of the world.

Jan 1, 1933

By Ancel St. John

During a session on coal and coke at the February, 1926, meeting of the American Institute of Mining and Metallurgical Engineers, the writer called attention to the important work on the X-ray analysis of coal1,2 being carried on in England by C. Norman Kemp and his associates. This aroused so much interest that a paper on the subject was requested for the October meeting. It has seemed advisable to make this paper a preliminary survey of the present status in the application of X-ray methods to coal problems and to follow it from time to time with further articles as the art develops. A survey of this sort naturally divides itself into two parts, radio-scopic analysis of the distribution of constituents through the body of the coal, and diffraction analysis of the state of association of the elementary components. In this article the subject matter concerning radioscopic analysis has been drawn almost entirely from the writings of Kemp and his associates and the illustrations have been sptcially furnished by him. It is a pleasure to record here a great indebtedness for this courtesy and cooperation. The subject matter and illustrations concerning diffraction analysis are taken from the author's unpublished researches. Nature and Properties of X-rays Before proceeding it is well to recall the nature and some of the properties of X-rays, as well as our present conception of atomic structure According to the accepted theory atoms are composed of electrically-charged particles. A positively-charged center, called the nucleus,

Jan 1, 1927

By F. E. Bash

Constantan is an alloy of copper and nickel that is extensively used, under a number of trade names, as a resistance wire with a low temperature coefficient of resistance, and one of the elements of base-metal thermocouples, iron usually being the other thermoelement, although for low-temperature work copper is also used. Before the war, constantan was imported, in common with many other technical necessities. Since it required considerable time to receive the constantan after it was ordered, fairly large stocks were kept on hand; but after the beginning of the war no more was imported and the stocks of foreign material were exhausted about the same time that the steel and munition manufacturers began to need great quantities of it for thermocouples for the heat treatment of steel. To meet this demand, the International Nickel Co. began manufacturing constantan that met all the requirements of the users of resistance wire but did not give the same electromotive force against iron as the German material and consequently could not be used with instruments calibrated for a definite e.m.f.-temperature relation. It so happened that all the constantan made had an e.m.f. lower than that necessary to meet the specifications of the Leeds & Northrup Co. for whom this investigation was carried out. If some had been higher and some lower, good wire could have been obtained by a process of selection, but as it was no wire at all could be procured. To remedy this situation, a thorough investigation was started with the close cooperation of the International Nickel Co. and the Electrical Alloys Co. The specifications to which the constantan had to conform were that it should give an e.m.f. of 47.40 millivolts against pure iron at 1500" F. (816" C.) with the cold-junction temperature at 0" F., or a proportional e.m.f. at temperatures near 1500" F. The method of checking a wire was as follows: It was first welded to a piece of iron wire; Armco iron was found to be satisfactory but iron with greater than 0.1 per cent. carbon would give a lower e.m.f. against the same piece of constantan than pure iron. The couple was then insulated and the fire end was tied to the

Jan 1, 1921

By Kurt Stock

The war caused a demand for enormous quantities of high-grade zinc, which were not available and could not be produced from pure ores in sufficient amounts and in the time required. Redistillation of virgin spelter on a large scale was practiced to supply this demand; this paper gives a full description of the process used by the Oklahoma smelters of the Bartlesville Zinc Co. As the redistillation of zinc has become of historical interest only, having been superseded by the electrolytic process, it was deemed advisable to give expression to this phase of the metallurgy of zinc that, in the past, had never gone beyond laboratory experimentation. THE grades of spelter demanded by the consuming industries were not definitely established until the American Society for Testing Materials undertook to fix specifications, based on the varying percentages of the common impurities (lead, iron, and cadmium) as follows: TOTAL, NOT LEAD, IRON, CADMIUM, OVER. PER PER CENT. PER CENT. PER CENT. CENT. A. High grade 0.07 0.03 0.05 0.10 B. Intermediate 0.20 0.03 0.50 0.50 C. Brass special 0.75 0.04 0.75 1.20 D. Prime western 1.50 0.08 The question which grade was the best for certain purposes and why was left unanswered. The conservatism of the zinc-smelting industry and the unwillingness of the spelter-consuming industries to engage in research work prevented the full benefits being obtained that such standardization promised. The custom smelters, producing spelter in pigs or plates, found it impossible to adhere closely to the established limits on account of the variety of ores treated; and the smelters with long-established and known brands, or those manufacturing their metal into marketable products, like sheet zinc, did not have to abide by the newly established grades based on chemical percentages.

Jan 7, 1924

By J. R. Szedon, T. L. Chu, G. A. Gruber

Amorphous adherent filnzs of silicon dioxide have been deposited on silicon substrates by the oxidation of silane at temperatures ranging from 650 to 1050C. Various diluents (argon, nitrogen, hydrogen) were used to suppress the formation of SiO2 in the gas phase. Deposition rates of the oxide were determined over the temperature range in question as functions of' re-actant flow rates. Etch rate studies were used for a cursory comparison of structural properties of deposited and thermally grown oxides. From electrical evaluation of metal-insulator-silicon capacitors it was determined that the interface charge density of deposited films is similar go that of dry-oxygen-grown films in the 850° to 1050 C temperature range. Deposited films exhibit several ionic instability effects which differ in detail from those reported for thermal oxides. Stable passivating films of silicon nitride over deposited oxides appear to be practical for use in silicon planar device fabrication. Such films can be prepared under temperature conditions which have less effect on substrate impurity distributions than in the case of grown oxides. AMORPHOUS silicon dioxide (silica) is compatible with silicon in electrical properties and is the most widely used dielectric in silicon devices at present. Silica films can be prepared by the oxidation of silicon or deposited on silicon or other substrate surfaces by chemical reactions or vacuum techniques. The ability of thermally grown silicon dioxide films to passivate silicon surfaces forms one of the practical bases of the planar device technology. Properly produced and treated films of grown SiO 2 can have low densities of interface charge (-1 X 10" charges per sq cm) and can be stable as regards fast migrating ionic sgecies. 1 To maintain these properties, even with an otherwise hermetically sealed ambient, the Sia layers must be at least l000 A thick. Such thicknesses require oxidation in dry oxygen for periods of 7.8 hr at 900°C or 2 hr at 1000°C. Although oxidation in steam or wet oxygen can reduce these times to 17 and 5 min, the resulting oxides must be annealed to produce acceptable levels of interface charge., Oxidation or annealing involving moderate to high temperatures for extended periods of time can be undesirable. Under some conditions, there can be changes in the distribution of impurities within the underlying substrate. A chemical deposition technique using gaseous am-bients is particularly attractive and flexible for preparing oxide films. With a wide range of deposition rates available, films can be produced under condi- tions of time and temperature less detrimental to impurity distributions in the silicon than in the case of thermal oxidation. The pyrolysis of alkoxysilanes, the hydrolysis of silicon halides, and various modifications of these reactions are most commonly used for the deposition of silica films.3 Silica films obtained in this manner are likely to be contaminated by the by-products of the reaction, organic impurities, or hydrogen halides. The use of the oxidation of silane for the deposition process has been reported recently.4 The deposition of silica films on single-crystal silicon substrates by the oxidation of silane in a gas flow system has been studied in this work. The deposition variables studied were the crystallographic orientation of the substrate surface, the substrate temperature, and the nature of the diluent gas. The electrical charge behavior of Si-SiO2-A1 structures prepared under various conditions was investigated by capacitance-voltage (C-V) measurements of metal-insulator-semiconductor (MIS) capacitors. The experimental approaches and results are discussed in this paper. 1) DEPOSITION OF SILICA FILMS The overall reaction for the oxidation of silane is: The equilibrium constants of this reaction in the temperature range 500° to 1500°K, calculated from the JANAF thermochemical data,= are shown in Fig. 1. In addition to the large equilibrium constants, the oxidation of silane is also kinetically feasible at room temperature and above. However, the strong reactivity of silane toward oxygen tends to promote the nucleation of silica in the gas phase through homogeneous reactions, and the deposition of this silica on the substrate would yield nonadherent material. The formation of silica in the gas phase can be reduced by using low partial pressures of the reactants. Argon, hydrogen, and nitrogen were used as diluents in this work. 1.1) Experimental. The deposition of silica films by the oxidation of silane was carried out in a gas flow system using an apparatus shown schematically in Fig. 2. Appropriate flow meters and valves were used to control the flow of various reactants, i.e., argon, hydrogen, nitrogen, oxygen, and silane. Semiconductor-grade silane, argon of 99.999 pct minimum purity, oxygen of 99.95 pct minimum purity, and nitrogen of 99.997 pct minimum purity, all purchased from the Matheson Co., were used without further purification. In several instances, a silicon nitride film was deposited over the silica film. This was achieved by the nitridation of silane with ammonia using anhydrous ammonia of better than 99.99 pct purity supplied by the Matheson CO.' The reactant mixture of the desired composition was passed through a Millipore filter into a horizontal water-cooled fused silica tube of 55 mm

Jan 1, 1969

By J. R. Mihalisin

Phase changes in as-cast alloys in the Ni2 CoCr-Ni, Ti-NSAl system containing 0.1 wt pct C were studied after heat treatment at 1650°F. It was found that a vegion of CrCo-type s was developed in this system after I1000 hr. The tendency for s formation was dePendent upon the aluminum and litanium content, the s -forming tendency generally becoming more pro-nounced as the latter two elements are increased. s lended to form in interdendritic regioues and was associated with solutioning- of- carbide phases. Electron- vacancy computations for prediction of s formation on these alloys mere in sufficient agreement with what was observed experimentally to indicate that the method should be of value in assessing a-forming potential in cast alloys. However, the correlation of electrotz- vacancy numbers may not be as favorable in cast as cormpared to wrought alloys. THE increasing use of high-temperature alloys for longer times at higher temperatures has resulted in a real need for obtaining information on the phase changes taking place in these alloys since these changes often have a direct effect on properties. This paper reports on a study of the phase changes in Ni-Cr-Co-Al-Ti alloys after prolonged heating at 1650°F. The alloys were selected from the pseudo-ternary system Ni2CoCr-Ni3Ti-Ni3Al and this system was chosen because it is the basis of many of the newer cast commercial superalloys. The attempt here was not to define accurately the boundaries of s formation in the NizCoCr-Ni3Ti-Ni3Al system but to delineate the phase transformations taking place upon heating alloys covering a wide range of chemistries in this system. An addition of carbon was made to all alloys to further simulate commercial alloys. It was hoped that the information generated in this manner would be of more direct use to superalloy designers than an equilibrium diagram approach since commercial alloys generally have outlived their usefulness when equilibrium is attained. EXPERIMENTAL PROCEDURE The alloys were vacuum-melted from carbonyl-nickel pellet, vacuum-grade chromium, electrolytic cobalt, high-purity aluminum and titanium, and spec-trographic-grade carbon.

Jan 1, 1968

By MARK H. LAMB

(Canal Zone Meeting, November, 1910.) THE recent growth of a sentiment among cyanide-plant designers against the use of gravity-stamps for the crushing preliminary to cyanidation may be said to date from the almost simultaneous perfection of the ribbed tube-mill liner and of the tall, air-agitation tank. The first step in the resulting change of practice was the universal adoption of the tube-mill for fine-grinding and the use of coarse screening oil the battery. This was the beginning of the surrender of supremacy by the gravity-stamp ; since merely the single fact that it was a more economical machine for crushing fine had retained it in favor as compared with ball-mills, rolls, or steam-stamps. The surrender, however, is not yet complete. It is the universal practice to use rolls where a relatively small tonnage is to be crushed coarse, as, for example, when coarse concentration is included in the plan of treatment. Power, attendance, repairs, and first-cost are smaller for the rolls, under such circumstances, than for stamps; and it is becoming daily more apparent that, with no concentration to provide for, the use of rolls and tube-mills, without the complication of trommels and elevators required by concentration, is rapidly gaining favor in the eyes of the leading designers. The next step was the use of the rapid-running Chilean mill between the gravity-stamps and the tube-mill, which again narrowed the field of operation of the gravity-stamp while radically widening its screen-aperture. Such a combination of stamps and Chilean mill offers advantages when fine concentration is necessary, since the reduction in the Chilean mill call be adjusted easily and governed by varying the screen-mesh. But even concentration is now looked at askance. One of the leaders of this metallurgy has abandoned the separation and

Jul 1, 1910

By T. R. Lippard

PURE gypsum may be broken down into its constituents as follows: [ ] Standard specifications (ASTM Designation C22-25) state that a material shall not be considered gypsum if it contains less than 64.5 pct by weight of CaS042H2O. Anhydrite, the second calcium sulphate mineral found in nature, may be broken into its constituents as follows: [ ] PROPERTIES OF GYPSUM AND ANHYDRITE Pure gypsum is colorless to white but various impurities change its color to shades of gray, brown, red, or pink. It has a hardness of 2 in the Mohs scale and can be scratched with the fingernail. The specific gravity of pure gypsum is 2.3 to 2.4, so that rock gypsum, free from moisture, weighs about 145 lb per cu ft. Gypsum crystallizes in the monoclinic system in tabular crystals that exhibit good cleavage

Jan 1, 1949

By G. K. Manning, A. R. Elsea, C. R. Simcoe

Boron increases the hardenability of hypoeutectoid steels by decreasing the nucleation rate of ferrite and bainite. It is postulated that concentrations of lattice imperfections, such as exist at the grain boundaries, furnish the necessary energy for nucleus formation. Boron, because of its atomic diameter, will concentrate at lattice imperfections where sites of suitable size are present. Boron will decrease the energy of these local areas by occupying these sites. This mechanism accounts for the large increase in hardenability observed with small amounts of boron. The loss of the boron hardenability effect and the boron precipitate formation are explained on the basis of increased concentration of boron at the grain boundaries either with increasing boron content of the material or with increasing temperature. COMMON alloying elements affect both the nucleation and growth rates of the austenite decomposition reactions.' This effect is largely a result of the slow diffusion rates of these elements. Although a small addition of boron markedly increases the hardenability of steel, the diffusion rate of boron, which is of the same order of magnitude as that of carbon, can hardly account for this effect. An addition of boron in the range of 0.001 to 0.003 pct is about as effective as an addition of 0.30 pct Mo, 0.40 pct Cr, or 1.25 pct Ni in increasing the hardenability of a 0.40 pct C steel;' however, increasing the carbon content of the steel decreases the effectiveness of the boron addition."' The difficulty in understanding why so small an addition of boron can replace much larger quantities of the more strategic alloys, together with the erratic behavior sometimes encountered in boron-treated steels, has interfered with their general acceptance by industry. In the belief that an understanding of the mechanism by which boron increases the hardenability of steel should lead to a more general acceptance of boron-treated steels, a research investigation to determine this mechanism was undertaken at Battelle Memorial Institute under sponsorship of Wright Air Development Center. Experimental Work In order to study the effect of boron on the transformation of austenite to ferrite and bainite, a group of steels was made with a basic composition similar to that of the SAE 8600 series. This base composition was chosen because it has sufficient hardenability to permit accurate measurement of the times required for transformation to start at various temperatures. The chemical analyses of the steels used in the first part of this investigation are listed in Table I. These steels were made as 200 lb heats in an induction furnace. The furnace charge was Armco ingot iron with the alloying elements added as ferroalloys. After the alloy additions were made, the heat was deoxidized with 0.125 pct Al. A 100 lb ingot was cast and an addition of 0.003 pct B, as ferroboron, was made to the metal remaining in the furnace. This metal was cast into a second 100 lb ingot. The ingots were forged to 11/4 in. diam bar stock from which end-quench hardenability specimens were obtained. Part of this material was further reduced by hot rolling to lx¼ in. bar stock from which specimens were obtained for isothermal transformation studies. Studies of Nucleation and Growth: End-quench hardenability tests were performed on these steels, using an austenitizing temperature of 1600°F. The hardenability curves, shown in Fig. 1, indicate that boron treatment resulted in considerable increase in hardenability of the steels. Any such change in hardenability must result from a change in the transformation rate of the austenite, and these rate changes can be established readily by isothermal transformation studies. Isothermal transformation studies were conducted on these steels as follows: specimens were austeni-tized at 1600°F for 15 min, transferred to a lead bath operating at a constant subcritical or intercritical temperature, held for various lengths of time, and water quenched. The specimens were sectioned for metallographic examination to determine the amount and the type of transformation products present. In order to determine the effect of boron on the formation rate of ferrite, isothermal transformation tests were made on the 0.20 pct C steel in both the boron-treated and boron-free condition at an intercritical temperature of 1375°F where ferrite is the only decomposition product of this low carbon austenite. The results of these tests are shown in Fig. 2, where the percentage of ferrite formed is plotted as a function of time at temperature. It is apparent that boron markedly decreased the transformation rate of austenite to ferrite at this temperature.

Jan 1, 1956

By R. W. Kraft, L. D. Graham

The process of' spheroidization, or more properly coarsening, of Al-CuAl,eutectic alloy specimens with various initial microstructures was studied by quantitative metallographic and X-ray diffraction techniques. By measuring the rale at which specimens with a very fine dispersion of phases (produced by quenching molten droplets of the alloy in water) coarsened it uias determined that the rate-controlling mechanism for coarsening was diffusion, probably of aluminum in the aluminum-rich phase. The lamellae in specimens with a high degree of microstructural and cr-ystallog/uphic anisotropy (produced hy unidirectional solidification of ingots) thickened during heat treatment by recession of the CuAl, platelets from jaulted regzons, yet the specinlens retained a very high degree of. anisotropy after prolonged heat treatments at a temperature within 8°C of the eutectic temperature. In such specimens the crystallographic orientation relationship between the phases remained constant and no change in the crystallographic substructure occurred. Based on these observations a model was developed for the coarsening—or rate of' thicken-ing—oj- the lamellar structures which predicts that the rate of decrease of interface area is proportional to the square of lamellar interface area. Experiments with degenerate and very coarse lamellar microstruc -tures preduced by extremely slow unidirectional solidification) indicate that initial microstructure is a most important factor governing the final micro-structure after heat treatment. The particle size and shape of dispersed phases are important parameters affecting the properties of a wide variety of two-phase materials. As is well-known, varietythe dispersed-phase particles tend to coarsen at appropriately high temperatures because the interface energy of the system is reduced by the concomitant reduction in interface area. The phenomenon of

Jan 1, 1967

By Geo. T. Lynch

PALEOLITHIC MAN, laboriously shaping a stone implement in his cave, discovered that the dust irritated his eyes and nostrils and hindered his labors, whereupon, muttering a few incantations, forerunners of modern profanity, he removed himself and his work outside. There, ignoring the jeers of the hairy ?old-timers,? he turned his back to the wind and resumed operations in comparative comfort. Thus originated the dust problem in the mineral industries, and its solution. Despite long familiarity with the annoyance, danger, and loss occasioned by dust, little progress was made in the engineering solution of its problems until recent years. Some advance can now be reported but too many traces of ancient tradition and practice still remain. Considerable published information is available but only a part of this is of proved accuracy and utility. The greater portion is either misleading, being derived from too few cases to be of general application, or entirely erroneous, originating in guesswork, legend, or individual inspiration, divine or otherwise. The engineer, confronted with a dust problem, has neither the time nor the special training required to extract the values from this mass of low-grade. It is, therefore, desirable that we attempt to correlate the known values and to put them into a form upon which actual progress can be based. This discussion is, then, for the benefit of that engineer, particularly the engineer in the mineral industries and more particularly in ore-dressing plants, and is merely a gathering of facts already known but difficult to segregate.

Jan 1, 1938

By A. U. Seybolt

The pressure-temperature relations required to maintain the existence of Si3N4 in silicon-iron of 0.44-11.7 pet Si have been partially explored. The critical data obtained have allowed the calculation of some thermodynamic quantities, and have shown evidence of an order-disorder two-phase field extending at 800°C from about l pet to 5.5 pet Si. THE presence of silicon nitride in electrical sheet, nominally about 3 1/4 pet silicon, balance iron, has been described by several authors'" but there has been some discrepancy among them regarding the identity of the nitride. Also, little has been reported on the quantitative thermodynamic prop- erties. In the work to be reported here, the nitride has been found to be more stable than described by Corney and Turkdogan." Several silicon nitrides have been described in the past, including SiN, Si3N4 and Si2N4 (see, for example, Abegg6 and Pascal7). However, the literature on nitrides other than Si,N, is all very old. No recent investigators using the more powerful tools available today have reported the presence of any nitride other than S3,N4. W. B. Hicke and L. R. Brantley8 in 1930 determined the dissociation pressure of Si3N4 which they made by reacting nitrogen

Jan 1, 1959